This invention relates to pliers, and, more particularly, to a self-adjusting pliers that grips workpieces of various sizes without manual adjustment.
The traditional version of a pliers includes two elongated members joined at a pivot pin. One end of each elongated member forms a jaw, and the other end forms a handle. Workpieces of different sizes are grasped in different manners, due to the constant geometry of the elongated members and the jaws. Some adjustability may be achieved by providing a slotted receiver in one of the handles, so that the handle with the pivot pin may be moved between different positions in the slot to provide adjustability for gripping objects of different sizes.
U.S. Pat. No. 4,651,598 provides an improved pliers whose jaws are self adjusting according to the size of the workpiece. Commercial versions of this pliers are useful, but have important drawbacks. Perhaps the most significant problem with the pliers made according to the ""598 patent is that the jaws move relative to each other in an end-to-end manner as they are clamped down onto a workpiece. Soft workpieces such as brass or copper may be marred as a result. The clamping force applied by these pliers depends upon the size of the workpiece being grasped. Additionally, these pliers cannot be locked closed for convenient carrying and storage.
Another problem with the pliers of the ""598 patent is that they do not lock to the workpiece, an important convenience in some uses of pliers. Overcenter locking pliers are described in a series of patents such as U.S. Pat. No. 4,541,312. Conventional overcenter locking pliers provide adjustability in the size of the workpiece that may be gripped through a screw adjustment to the pivoting position of the control arm, but this adjustability is not automatic in the sense of the pliers of the ""598 patent.
Other types of locking pliers such as the AutoLock(trademark) pliers combine the self-adjusting feature with an overcenter locking mechanism. This pliers can be inconvenient to use for some sizes of workpieces, suffers from some of the problems of the pliers of the ""598 patent, does not achieve a large gripping force, and may unexpectedly unlock when large objects are being gripped.
There is a need for a self-adjusting pliers which does not experience shifting of the jaw position as the object is grasped, and which may be provided in a locking version. The present invention fulfills this need.
The present invention provides a self-adjusting pliers wherein the jaws automatically adjust to various sizes of workpieces. There is no end-to-end relative movement of the jaws as they grasp the workpiece, so that there can be no marring of the type observed with the pliers of the ""598 patent. The clamping force is substantially constant regardless of the size of the workpiece, but is adjustable in some versions of the pliers. The clamping force is multiplied several times by the mechanism, leading to a much higher maximum available clamping force than possible with conventional pliers. The pliers may be provided with no locking or with releasable overcenter locking, or with the ability to switch between the two.
In accordance with the invention, a self-adjusting pliers comprises an upper arm including an upper jaw at a first end thereof, an upper handle at a second end thereof, a support extending downwardly from an intermediate location thereof between the first end and the second end, a downwardly extending guide on the support, and a downwardly extending slot on the support, the downwardly extending slot being parallel to the downwardly extending guide. A lower arm includes a first end thereof and a lower handle at a second end thereof. A control arm is pivotably connected at a first end to the upper arm at a location adjacent to the second end of the upper arm, and at a second end to the lower arm at an intermediate location between the first end and the second end thereof. A spring is affixed between the upper arm and the control arm so as to resist rotation of the control arm. A lower jaw member includes a lower jaw at a first end thereof, the lower jaw being in a facing relationship to the upper jaw, and a slider extending from a side of the lower jaw member, the slider being slidable on the guide of the support. A locking engagement is disposed to controllably engage the downwardly extending slot upon pivoting movement of the lower handle to an overcenter position. A shifter has three pivot points arranged in a triangular pattern, the three pivot points being respectively connected to the lower jaw member, to the locking engagement, and to the first end of the lower arm.
The lower jaw member is not part of or rigidly fixed to the lower arm, but is linked to the lower arm by a linkage. The lower jaw member slides in the first slot, so that it necessarily produces a controlled clamping force and clamping direction on the workpiece being grasped. The lower jaw member cannot move in a sideways or end-to-end fashion, thereby overcoming a significant fault in some prior self-adjusting pliers. The locking and clamping force is applied by the user""s hand force through the two handles and thence through the locking engagement mechanism acting against the sides of the slot and through the rigid-body pivoting shifter. The two functions of the guiding of the movement of the lower jaw member and the application of force are thus separated to ensure that the movement of the lower jaw member is true.
The guide and the slot may be straight or curved. When they are straight and parallel, the force applied to the workpiece being grasped is approximately constant, but varies slightly for different sizes of workpieces. When they are curved and parallel, it is preferred that the guide slot and the slot are each curved with respective curvatures of substantially constant radius from the upper control arm pivot pin. In this case, the force applied to a workpiece is substantially constant for all sizes of workpieces, an important advantage for some applications.
The maximum magnitude of the clamping force applied to the workpiece may be much larger than possible with conventional pliers, due to four stages of force multiplication present in the mechanism. The length of the handles, the angle between the control arm and the lower arm, the relative location of the shifter pins, and the movement of the shifter relative to the jaw mechanism all contribute to a leveraged four-stage multiplication of the force applied though the handles. The multiplication factors are established by the structural geometry built into the pliers.
The pliers may also be provided with control over the clamping force applied to the workpiece through the jaws. A manual force adjuster acting on the control arm is provided at a location adjacent to the first end of the control arm. The manual force adjuster is operable to move the upper control arm pivot pin of the control arm in a direction along the length of the upper arm. This movement of the first end of the control arm changes its angle and position relative to the lower arm and to the jaw member, with the result that the clamping force applied through the jaws is controllably variable.
In one embodiment, the pliers include a releasable overcenter lock for the jaws. In this version, there is a downwardly extending lobe on the control arm. A release arm is pivotably connected to the lower arm and has a release pad disposed to contact the lobe of the control arm when the release arm is pivoted. In operation, the control arm moves to an overcenter position when the clamping force is fully applied. This overcenter position may be released to unlock the jaws from the workpiece either by pulling the handles apart, or by manually pivoting the release arm. The overcenter locking is readily released by pulling the handles apart when the clamping force is small, but is more conveniently released by operating the release arm when the clamping force is large.
In another version, the pliers is controllably switchable between a non-locking function and a locking function. An overcenter lock switch mechanism in the lower handle is movable between a first position whereat the overcenter lock switch mechanism does not prevent pivoting movement of the lower arm relative to the control arm prior to reaching an overcenter lock, and a second position whereat the overcenter lock switch mechanism does prevent pivoting movement of the lower arm relative to the control arm prior to reaching an overcenter lock. The movement of the locking switch mechanism to the second position prevents the pivoting movement of the lower arm and the control arm to an overcenter locking position, and thereby prevents this overcenter locking function.
It is preferred to combine the features of the manual force adjuster and the releasable overcenter lock in a single pliers, when either feature is provided.
The clamping mechanism of the invention is operable to move the lower jaw member upwardly along the downwardly extending guide until the lower jaw contacts the workpiece, thereafter to lock the lower jaw member to the downwardly extending slot, and to transfer a clamping force to the lower jaw. The clamping mechanism is thus self-adjusting to accommodate any size workpiece that will fit between the jaws. The lower jaw member and the lower jaw are constrained to move along the guide, independent of the functioning of the locking feature that operates in conjunction with the slot, ensuring a true movement. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.